While methods of diagnosis of eye disease depend to a considerable extent on determining abnormalities of vision, the patient's attention is in general confined to those parts of the images of the outside world which fall on a small central region of the light-sensitive retina, known as the fovea or macula. However, many diseases may start at random anywhere on the retina, and the patient is then unaware of any defect. The standard test of visual acuity depends upon foveal function, and is now recognized to be insufficient as a means of describing vision and its defects. Therefore, other pieces of equipment called generically perimeters have been devised to test function at all other points in the retina (known as the peripheral and paramacular retina). What these have in common is that the locus of a point or points in the retina in which function is altered are specified. To test vision with such equipment takes considerable time and it is difficult for the patient to cooperate.